Liquefaction and separation of the constituents of gaseous mixtures



Aug. 11, 1925. 1,548,860

c. c. VAN NUYS LIQ UEFACTION AND SEPARATION OF THE CONSTITUENTS OF GASEOUS MIXTURES Filed Sept. 9, 1,920

whoa M 0145 w a Patented Aug. 11, 1925.

UNITED STATES PATENT OFFICE.

CLAUDE C. VAN NUYS, OF NEW YORK, N. Y., ASSIGNOR TO AIR REDUCTION COMPANY, INC., A. CORPORATION OF NEW YORK.

LIQUEFACTION AND SEPARATION OF THE CONSTITUENTS OF GASEO'US MIXTURES.

Application filedSeptember 9, 1920. Serial No. 409,197.

To all 7011 om it may concern:

Be it known that I, CLAUDE C. VAN More, a citizen of the United States, residing at New York city, in the county of New York, State of New York, have invented certain new and useful Improvements in Liquefaction and Separation of the Constituents of Gaseous Mixtures; and I do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same.

This invention'relatcs to the liquefaction of gases for the purpose of separating the constituents thereof by rectification.

In liquefaction methods as heretofore employed, the advantages of partial liquefaction and auto-purification by a backward return of the liquid in contact with the gas has been advantageously employed to produce a liquid enriched in a less volatile constituent of the mixture, which liquid is subsequently subjected to rectification to separate the more volatile constituent. In such a method, the liquid originally formed should have a composition approximately in phase equilibrium with the gaseous mixture which is to be treated. It has been found,

- however, that a simple liquefaction with backward return does not permit of sufficientseparation of the gaseous constituents to insure a liquid having the composition desired to attain the highest efficiency. Thus, in the separation of oxygen from nitrogen in the atniosphere, the liquid formed should contain approxin'iately 47% oxygen, but it has been impossibe heretofore to produce such a liquid, because as has been discovered, the volume of liquid returning and particularly at the lower ends of the condensing tubes is such and its rate of travel is so high that no opportunity is afforded for the desired separation. In a well-known method employing this principle of condensation with backward return, there is an addition to the difficulty just mentioned, the further disadvantage that the enrichment in the less volatile con stituent obtained by backward return is reduced by the addition to the liquid delivered by the backward return condenser of a certain amount of unenric-hed liquid air in order to make up losses of liquid due to heat leakage. Since the liquid is delivered to a rectifier in which the final separation of the constituents is accomplished and governs more or less the composition of the effluent gas, it will be appreciated that the provision of an initial liquid of the desired com position is of the highest importance in the successful and eflicient recovery of constituents of gaseous mixtures.

The object of the present invention is, therefore, to provide a method of and apparatus for separating the constituents of gaseous mixtures in which an initial liquid is produced having substantially the theoretically possible composition of the liquid in phase equilibrium with the incoming air.

Further objects and advantages of the invention will be apparent as it is better understood by reference to the following specification when read in connection with the accompanying drawing which diagrammatically illustrates an apparatus adapted to the accomplishment of the desired object.

It is to be understood that while the apparatus illustrated is that preferably em ployed in carrying out the invention, various modifications may be introduced and no attempt has been made to illustrate details which may be readily supplied by those skilled in the art. Furthermore, while the invention will be described more particularly with reference to the separation of oxygen and nitrogen from air, the method and apparatus are applicable to the treatment of gaseous mixtures in general and no limitation is implied, therefore, by reference to the atmosphere and the constituents thereof. In describing the method and apparatus, the atmosphere will be considered as comprising oxygen and nitrogen, thereby disregarding the rare elements present, since these elements do not materially affect the operation so far as the production of commercial gases is concerned.

In carrying outthe intention, air is delivered after it has been compressed and cooled in the usual manner to an apparatus in which it is subjected to indirect contact with colder liquid and gaseous products, the liquids being held at somewhat lower pressures so that they are permitted to evaporate through transfer of heat from the incoming air. A portion of the air is thus liquefied and this portion consisting of substantially all of the oxygen with some of the nitrogen flows backwardly within tubes provided in the apparatus, as hereinafter described, in

contact with further portions of the air ascending in the tubes, and tends during its backward passage, to become enriched in oxygen while a portion of the nitrogen is talitn u and carried away with the residual unliquehed portion of the air. This residual gas is substantially pure nitrogen and in the preferred embodiment of my invention, the nitrogen is withdrawn and may be applied to any desired purpose after its cold has been transferred to incoming air. The nitrogen being delivered at the initial pressure of the air, may, after it is warmed, be expanded in a suitable engine in order to assist in providing the requisite amount of refrigeration and to recover a portion of the energy originally expended in compressing the air. A portion or all of the nitrogen may, however, be liquefied and delivered to the rectification column. This mode of applying the invent-ion is not, however. considered in detail in the present embodiment, the invention being more particularly directed to the method of and means whereby liquid ofthe desired composition may be accumulated.

The liquid escaping from the tubes in which it is formed is, for the purpose of the present invention, permitted to fall upon trays where it is subjected in relatively thin layers to the action of the incoming air for the purpose of carrying out a partial rectification by contact of the air therewith and consequent separation of the more volatile constituent, nitrogen while oxygen from the air is liquefied and remains with the liquid. This liquid in passing over the trays is gradually enriched in oxygen and finally accumulates in a body which approximates a composition in phase equilibrium with the incoming air and contains, therefore, substantially 47% of oxygen, the remainder being nitrogen.

Liquid accumulated in this manner is delivered through a reducing valve to a rectifier where it is subjected to direct contact ith vapors arisin from the liquid evaporated by the initiaT condensation of the air. By this means, the constituents are separated, the oxygen accumulating in the liquid while nitrogen and a portion of the oxygen is released and the two gases escape as an eflluent having a composition in phase equilibrium with the liquid delivered to the rectifier. Since this liquid is materially enriched in oxygen, the liquid which finally accumulates as a result of the rectification will be correspondingly richer in oxygen and the gaseous oxygen produced by evaporation thereof will be of the highest quality and adapted to the most refined uses. The liquid oxygen which accumulates in the apparatus and is there vaporized is delivered in an extremely cold condition, and the pressure at which air enters the cycle may be high enough so that the oxygen is still at a relatively high pressure, although the originalpressure is somewhat reduced by the passage of the li uid through the reducing valve. After giving up its cold to the incoming air, the oxygen may, if at a relatively high pressure, be expanded in suitable engines in order to assist in the refrigeration and to recover a portion of the energy which was initially used in compressing the air.

Obviously while the particular feature of rectification to produce a liquid initially rich in oxygen is described herein in connection with numerous details of a method to which it is particularly adapted, it may be employed in connection with other methods requiring the delivery of a liquid mixture to a rectifier. My invention comprises the method of producing this initially enriched liquid whether or not it is applied to the specific method of separating gases as here inafter described.

Referring to the drawing for the more particular features of the invention, 5 indicates a column having a pot 6, a preliminary rectifier 7, a gas chamber 8, a liquid chamber 9 in which a receptacle 10 for liquid is suspended, and a rectifying compartment 11. Cold compressed air is delivered to the pot 6 through a pipe 12 and passes thence through trays 13 upon which the liquid fraction of the compressed air accumulates. The air thence passes through tubes 14.- in indirect contact with cold gaseous products of the operation in the chamber 8 and with liquid in the chamber 9 and receptacle 10 which cools the air to such an extent that substantially all of the oxygen and some of the nitrogen are liquefied. The tubes 14: terminate in a head 15 from which the residual gas consisting substantially of nitrogen is delivered through a pipe 21.

During its passage backwardly through the tubes in contact with the air, the liquefied fraction of the air is subjected to autopurifieation, the air taking up nitrogen. from the liquid and supplying oxygen thereto so that the liquid is gradually enriched in oxygen until it is delivered to the trays 13. Here enrichment in oxygen is augmented by the action of the incoming air which drives off a considerable proportion of the remaining nitrogen from the liquid while oxygen from the air is liquefied therefrom and joins the liquid which flows into the pot 6. This liquid accumulating in the pot has a compositlon which is substantially in phase equilibrium with the incoming air, the proportion of oxygen being substantially 47%, the maximum theoretical composition which is obtainable under the conditions prevailing.

From the pot 6 the liquid is delivered through a pipe 17 and reducing valve 18 to 4 vaporized while the liquid becomes more and more enriched in oxygen, being finally delivered through a pipe 20 to the receptacle whence it overflows into the chamber 9.

' The liquid accumulating-.in'the chamber .9

ized and withdrawn through the pipe 16. After giving up its cold to the incoming air, it may be expanded in a suitable engine to recover a portion of. the workoriginally applied in raising the airto its initial pres-1',

sure. The efliuent gas consisting principally of nitrogen with some oxygen necessarily f carried over by the inherent disability'of.

the rectification method to separate 3 the oxygen and nitrogen sharply, is delivered through a pipe 22.

To provide for heat interchange between the incoming air and the gases leaving the apparatus, an exchanger is employed com prising a plurality of sections A, B, G and- D which are substantially identical in form being provided with bafiles 23 and sets of tubes-24 and 25 which communicate with compartments 26, 27, 28 and 29 for the purpose of conveying the gases in indirect contact with'the incoming air circulating about the bafiies 23 and around the tubes. The sections of the exchanger are connected by pipes 30, 31 and 32 so that the air entering the exchanger is permitted to pass through the sections successively and is finally delivered through the pipe 12 to.the column.

Nitrogen delivered by the pipe 21 from the column enters the compartment 26 of the section D and travels successively through compartments D and C connected by a pipe 33. The nitrogen is withdrawn from the compartment 26 at the end of the section C and a portion thereof is delivered by a pipe 34 having a valve 35 to an engine 36 Where the gas is expanded and thereby cooled. The cold expanded product passes thence through a pipe 37 to the chamber 8 of the column where it circulates around the baffles 38 therein and about the tubes 14 for the purposes hereinbefore described. Escaping from the chamber 8, the gas is delivered through a pipe 39 to the compartment 27 at the end of the section D of the exchanger and passes through the tubes 25 of the several sections of the exchanger to the compartment '27 at the end of section A from which it escapes through a pipe 40 controlled by a valve 41.

The remaining nitrogen is conveyed through a pipe 42 to the compartment 26 in section B of the exchanger and passes through the through the tubes 24 in sections A and T5 which are connected by a pipe 43. The" nitrogen is delivered to the compartment -26'at the end of changer and is conveyed through a pipe 44 the section A of the excontrolled by a .valve' 45t0 anexpansion; engine 46 Where'the'nitrogen is expanded and thereby cooled. The cooled nitrogen is conveyed from the engine by a pipe 47 and a portion thereof'is delivered through.

a pipe 48' to the compartment 27 of the secpreviously expanded nitrogen from the en tion- B of the exchangerwhere it joins the: is substantially pure oxygen and 1s vaporgine 36 and is delivered therewith tothe outlet 40. Another portion .ofthe nitrogen from the engine 46 I changer 51 where incoming air deliveredpto the exchanger through an lntake 53. 7

is. conyeyed' througha pipe 49 controlled by a valve 50 'to an exit serves 'in' passing through the tubes'52 thereof to cool the 165 The nitrogen escapes through an outlet-54.

Oxygen from the column is delivered 29 at the end of'section D of the exchanger and 25 in the successive sectlons and is 'delivered through a pipe 55 trolled by-a valve 59 connects the pipe- 55 to, the pipe 44-so that in starting the apparatus, air after compression and passage through the apparatus, may be expanded in the engine '46 to produce the necessary refrigerating efl'ect.

The etliuent gas from the column passes through the pipe 22 to the compartment 28 at the end of the exchanger and thence travels through tubes 25 in the successive sections to the compartment 28 at the end of the section A of the exchanger. The effluent gas is withdrawn through a pipe 59' controlled by av valve 60 and in the normal operation of the apparatus is conveyed through a'pipe 61 controlled by a valve 62 to the inlet pipe 63 of the air compressor 64. The pipe 63 is connected to the exchanger 51 and receives the air cooled therein for conveyance .to the compressor. By permitting the efliuent gas from the column to mix with this incoming air, the temperature of the air may be further reduced before compression with corresponding advantage in the energy required for compression and, moreover, the effluent gas is returned to the cycle so that all of the air initially compressed is eventually separated and the constituents thereof are recovered.

The air or gaseous mixture compressed in the compressor 64 is cooled in an aftercooler 65 and is conveyed through a pipe 66 to the section A of the exchanger. After passing through the several sections in contact with the tubes 24 and 25, the air is delivered as hereinbefore described through pipe 16 to the compartmentpasses thencethrough tubesv to an outlet 56'co nit trolled by a valve 57. A. by-pass 58 eon-1 the pipe 12 to a pot 6 at the bottom of the column. To assist in accumulating refrigerative effect in commencing the operation, a by-pass 67 connects the pipes 59' and 34 and is controlled by a valve 68. Then the valve 68 is open and the valve 62 is closed, the effluent from the top of the column which in starting consists of air passing through the apparatus, is delivered to the engine 36 where it is expanded and cooled.

From the foregoing description, it will be apparent that I have introduced a novel feature with resulting improvement of liquefaction operations as heretofore conducted. By providing for rectification of the liquid initially formed in the apparatus before it is conveyed to the rectifier, the initial composition of this liquid in oxygen, for example, is markedly improved with the result that a closer and more economical separation is possible in the rectifier. This result is obtained whether the primary rectification is carried out in the apparatus disclosed or in the operation of other methods requiring the accumulation of a liquid rich in one constituent which is thereafter subjccted to rectification to separate two of the principal constituents thereof. Other novel features of the invention are found in the method of handling the gases subsequent to liquefaction and in the provision of means permitting expansion of these gases and the return of the effluent gas from the column for further separation.

Various changes may be in the method and apparatus disclosed without departing from the invention or sacrificing any of the advantages thereof.

I claim:

1. A method of separating the constituents of a gaseous mixture by liquefaction and rectification which comprises, subjecting the mixture to selective liquefaction with backward return to separate a liquid enriched in one of the constituents, rectifying the liquid when it is no longer subject to the cooling effect required for selective liquefaction by permitting the incoming mixture to pass therethrough and continuing the rectification with vapors from pre-' ceding portions thereof.

2. A method of separating the constituents of a gaseous mixture by liquefaction and rectification which comprises, subjecting the mixture to selective liquefaction with backward return to separate a liquid enriched in one of the constituents, rectifying the liquid while it is disposed in a plurality of layers and when it is no longer subject to the cooling effect required for selective liquefaction by permitting the incoming mixture to pass therethrough, and continuing the rectification with vapors released from preceding portions thereof.

3. A method of separating the constituents of a gaseous mixture by liquefaction and rectification which comprises, subjecting the mixture to selective liquefaction with backward return and auto purification to separate a liquid enriched in one of the constituents, subjecting the liquid thus enriched to preliminary rectification when it is no longer subject to the cooling effect required for selective liquefaction by contact with the incoming mixture and continuing the rectification with vapors released from preceding portions thereof.

4c. A method of separating the constituents of a gaseous mixture by liquefaction and rectification which comprises compressing and cooling the mixture, subjectin the mixture to selective liquefaction with ackward return and auto purification to separate a liquid enriched in one of the constituents, subjecting the liquid thus enriched to preliminary rectification when it is no longer subject to the cooling effect required for selective liquefaction by contact with the incoming mixture at its initial pressure, reducing the pressure on the liquid and contin'uing the rectification with; vapors released from preceding portions thereof.

5. A method of separating the constituents of a gaseous mixture by liquefaction and rectification which comprises, compressing and cooling the mixture, subjecting the mixture at its initial pressure to selective liquefaction with backward return and auto purification to separate a liquid enriched in one of the constitutents and a residual gas, withdrawin the residual gas, subjecting the enriched fiiquid when it is no longer subject to the cooling effect required for. selective liquefaction to preliminary rectification with the incoming mixture at its intitial pressure, and continuing the rectification with vapors released from preceding portions thereof. I

6. A method of separating the constituents of a gaseous mixture by liquefaction and rectification which comprises, compressing and cooling the mixture, subjecting the mixture at its intitial pressure to selective liquefaction with backward return and auto purification to separate a liquid enriched in one of the constituents and a residual gas, withdrawing the residual gas, subjecting the enriched liquid when it is no longer subject to the cooling effect required for selective liquefaction to preliminary rectification with the incoming mixture at its initial pressure, continuing the rectification with vapors released from preceding portions thereof and utilizing the residual gas for the recovery of energy therefrom.

7. A method of separating the constituents of a gaseous mixture by liquefaction and rectification which comprises, compressing and cooling the mixture, subjecting the lid mixture at its initial pressure to selective liquefaction with backward return and auto purification to separate a liquid enriched in one of the constitutents and a residual gas, Withdrawing the residual gas, warming the residual gas by heat interchange with the incoming mixture, separately expanding portions of the residual gas to recover energy therefrom, subjecting the liquid when it is no longer subject to the cooling effect required for selective liquefaction to preliminary rectification with the incoming mixture at the initial pressure and continuing the rectification with vapors released from preceding portions thereof.

8. A method of separating the constituents of a gaseous mixture by liquefaction and rectification which comprises, compressing and cooling the mixture, subjecting the mixture at its initial pressure to selective liquefaction with backward return and auto purification to separate a liquid enriched in one of the constituents and a residual gas, withdrawing the residual gas, subject' the enriched liquid when it is no longer su ject to the cooling effect required for selective liquefaction to preliminary rectification wlth the incoming mixture, at its intitial pressure, continuing the rectification with vapors released from preceding portions thereof, Withdrawing an efiuent gas resulting from rectification and returning the efiuent gas with the incoming mixture.

9. A method of separating the constituents of a gaseous mixture by liquefaction and rectification which comprises subjecting the mixture to selective liquefaction by indirect contact with a body of liquid, separating thereby a li uid enriched in one of the constituents and a residual gas, withdrawing the residual gas, permitting the enriched liquid to flow backwardly in contact with the incoming mixture, subjecting the enriched liquid when it is no longer subfiject to the cooling effect required for selective liquefaction to a preliminary rec-' tification with the incoming mixture to produce a further enrichment, reducing the pressure on the enriched liquid and subjecting it to rectification with vapors arising from said body of liquid.

10. A method of separating the constituents of a gaseous mixture by liquefaction and rectification which comprises, subjecting the mixture to selective liquefaction by indirect contact with a body of liquid, separating thereby a liquid enriched in one of the constituents and a residual gas, withdrawing the residual gas, permitting the enriched liquid to flow backwardly in contact with the incoming mixture, subjecting the enriched liquid when it is no longer subject to the cooling efiect required for selective liquefaction to a preliminary rectification with the incoming mixture to produce a further enrichment, reducing the pressure on the enriched liquid, subjecting it to rectification with vapors arising from said bod of liquid and utilizing the residual gas for t e recovery of energy therefrom.

In testimony whereof I afiix my signature.

CLAUDE C. VAN NUYS. 

